Structure And Replication Of Nucleic Acids, Enzymes Involved In Dna Replication

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Structure and replication of nucleic acids, enzymes involved in DNA replication

The steps involved in DNA packaging in eukaryotic organisms

Throughout the cell cycle, chromatin undergoes very notable changes since the eukaryotic DNA is exactly combined with a large amount of protein. The condensed length eukaryotic chromosomes is due to the large amount of DNA, where each DNA consists of a double propeller and unique. DNA packaging is thanks to a multiple level system, below each step is described:

  1. DNA United to histones, forming nucleosomes: A nucleosome has eight histone molecules with the end of the tail each projection outward
  2. The nucleosomes form "accounts" about a "strand" of DNA: it occurs during the interface
  3. The nucleosomes are packaged in a spiral that is enrolled in another spiral and so on: it occurs during the profase
  4. The spirals are folding forming handles
  5. The handles are rolled and form chromosomes

 

A critical analysis of the characteristics of DNA and RNA to be considered the genetic material

Because nucleic acids are large molecules formed by nucleotides that perform essential functions in cell metabolism and ensure the transmission of genetic information from some cells to another. Nucleotides are the units that make.

In this sense, the characteristics that DNA and RNA must meet to be considered as the material in charge of carrying the biological inheritance are mainly: save information, allow to faithfully copy such information, enable some capacity to change, of alteration of it, in addition, in addition to carry out the protein synthesis process.

In 1944, Oswald Avery, C. Macleod and m. McCarty provided proof that this transforming factor was nucleic acids, that is, the genetic material of the cell are DNA and RNA.

In what sense the DNA is synthesized: 3 ’→ 5’, 5 ’→ 3’

Polymerase DNA (the enzymes in charge of synthesizing DNA) only know how to synthesize DNA in the 5 ′ – 3 ′ address. That is, they are only able to add nucleotides to the 3 ′ Oh end of another nucleotide triphosphate. Polymerase DNA need an end 3 ′ Oh to add tryphosphate nucleotides to begin DNA synthesis. A double DNA propeller is always antiparalle; In other words, a chain runs in 5 ′ to 3 ′, while the other runs from 3 ′ to 5 ′. This makes necessary that the two new chains, which are also antiparallel to their molds, occur in slightly different ways.

What is understood by bidirectional synthesis

Replication can be unidirectional or bidirectional, this is determined by the formation of one or two replication forks at the origin; In bidirectional replication, two forks are formed that move away from the origin in opposite directions; This is started at a point in the DNA molecule The process develops towards the two ends of the chain; In each loop, the ends or replication forks advance in the synthesis process until the copy is completed.

The biological meaning of the central dogma of molecular biology

The biological meaning of the central dogma of molecular biology presents great importance since thanks to Watson and Crick as great scientists of the twentieth century, the progress to this branch contributed significantly. From the biological point of view it is mainly based on the mating rules of the nitrogenous bases where the two chains made up of four different nucleotides, each constituted of a phosphate group a sugar (deoxyribose) and a nitrogenous base, with their respective mold and give rise to another new complementary in the cell division process and has a model of the transmission of hereditary information from generation to generation. Finally in the contributions of the initially mentioned scientists especially Crick contributed biology to stop being descriptive to be a fundamentally experimental science and check the studies.

Properties that a molecule must gather to be the hereditary material:

  • Store stable biological information
  • They double and go to the following generation
  • Somehow they control hereditary characters
  • Mutation and recombination

 

The stages of initiation, elongation and termination of the DNA replication process

Initiation phase: The origin of replication is a portion of DNA that contains a characteristic sequence of bases. This segment is recognized by a protein called DNA-A.

Elongation phase: The elongation consists of the formation of the primer and the synthesis of the DNA chain. The process is characterized by not developing identically in both strands. The synthesis in the conductive or continuous chain requires only that the primary acts forming an RNA primer of about 10 to 60 nucleotides, and then penetrate the DNA polymerase III and perform the polymerization of deoxyribonucleotides. In the delayed chain a protein set is formed in which seven different proteins are located in addition to prima (cousosome). This group moves along the delayed strand mold in 5 ′ → 3 ′ synthesizing at intervals a short RNA primer, which will be joined DNA formed by the DNA polymerase III. The fact that the work addresses of Prima dimérica. This enzyme forces the delayed strand mold to form a loop on the same. In this way, the direction of synthesis is the same in both strands. When the polymerization is developed, the loop increases until they contact the previous Okazaki fragment, forcing the polymerase to separate or dissociate and to recommend again the process where the new primer has formed and she will create the new loop. In a posterior phase, the Cebator RNA segments are eliminated, by action of the exonuclease activity 5 ’→ 3 ′ of the DNA polymerase I, who also is responsible for filling the pieces occupied by the primer. Finally, DNA ligase links segments catalyzing the formation of a phosphodiéster link.

Termination phase: The process ends when two replication forks are joined or reached in opposite directions.

If it is a circular DNA, the two resulting molecules will be ringed and will be required of a topoisomerase II to become independent. If this is linear DNA we will have problems at the ends of the chains since we cannot finish off the ends or that requires telomerases.

Replication is completed when replicas, which run around cell chromosome in contrary directions, are halfway.

The characteristics and functions of each of the enzymes involved in the replication of the DNA

DNA replication is a complex process that requires a variety of enzymes that form a functional complex and that fulfill specific functions. They are between them:

  • DNA polymerases: they are the main enzymes during the replication of genetic material. There are three types of DNA polymerase (I, II and III). Within its main functions are: Synthesize new DNA chains by complementarity of deoxyribonucleotides Tryphosphate (DNTP) with the mold, form phosphodiéster bonds between the nucleotides that make up the DNA chain and improve or correct the accuracy of the process of replication through the elimination of erroneous bases in the chain.
  • Baver: It is a short nucleic acid chain formed by 18 to 24 pairs of complementary bases to the mold. These small fragments of genetic material are very important because they act as a small base chain that allows DNA polymerase to initiate the synthesis of the new DNA chain in the DNA replication process. The enzymes in charge are synthesized the small priming chain are called premiums.
  • Helicases: is part of the functional group of enzymes that interact during DNA replication. Its main function is to divide the strands of the mother chain by separating the hydrogen bridges from its nitrogen bases. There are two types of helicases, those of RNA and DNA.
  • Nucleas: This enzyme is mainly responsible for breaking phosphodiester bonds between nucleotides. They are used to degrade genetic material in specific places in the DNA chain. There are two types of nucleasas and will be categorized depending on the nucleic acids that degrade, being ribonucleases (RNA) and deoxyribonucleas (DNA).
  • Topoisomerase: they are the most important enzymes of the functional group during replication since their function is to modify the form of the double dnus propeller. Topoisomera are characterized because they are responsible for ‘’ rolled ’’ or ‘’ unwind ’’ DNA strands to facilitate the process of replication of genetic material. There are four types of topoisomerase (I, II, III and IV).

 

How the Okazaki fragments are formed

Okazaki fragments are formed from a short RNA fragment called primer, which is synthesized by an enzyme called prima. The primer is synthesized on the lagged mold chain.

The DNA polymerase enzyme adds nucleotides to the previously synthesized RNA primer forming an okazaki fragment. The RNA segment is subsequently eliminated by another enzyme and then replaced by DNA.

Finally, Okazaki’s fragments join the growing DNA chain through the activity of an enzyme called Ligasa. Thus, the synthesis of the lagging chain occurs discontinuously because of its opposite orientation.

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